The present invention relates to a vehicle air conditioner, and more particularly, to a vehicle air conditioner that includes a variable displacement compressor.
The compressor in such a vehicle air conditioner according to the publication has a swash plate and is shown in FIG. 6. A housing 101 of the compressor includes a front housing member, a center housing member and a rear housing member. A crank chamber 102 is defined in the front housing member. Cylinder bores 113 are defined in the center housing member. A suction chamber 114 and a discharge chamber 115 are defined in the rear housing member. A valve plate 117 is located between the center housing member and the rear housing member. A drive shaft 103 extends through the crank chamber 102 and is supported by the front housing member and the rear housing member.
The drive shaft 103 is coupled to an external drive source, which is a vehicle engine Eg, by an electromagnetic clutch 105. The clutch 105 is attached to the front end (left end as viewed in the drawing) of the housing 101. The clutch 105 includes a pulley 106 and an armature 107. The pulley 106 rotates relative to the housing. The armature 107 is fixed to the drive shaft 103 to rotate integrally therewith. An electromagnet 108 is located in the pulley 106. When the electromagnet 108 (the clutch 105 is on) is excited, the armature 107 is attracted to the electromagnet 108 and pressed against the pulley 106, which transmits the power of the engine Eg to the drive shaft 103. When the electromagnetic 108 is de-excited (the clutch 105 is off), the armature 107 is separated from the pulley 106, which disconnects the drive shaft 103 from the engine Eg.
A lug plate 109 is arranged to the drive shaft 103 in the crank chamber 102. The lug plate 109 is fixed to the drive shaft 103 to rotate integrally with the drive shaft 103. The swash plate 110 is supported on the drive shaft 103 and inclines relative to the axis L of the drive shaft 103. The swash plate 110 is coupled to the lug plate 109 by a hinge mechanism 111. A ring 112 is fitted about the drive shaft 103 to prevent the swash plate 110 from moving beyond the minimum inclination position. When contacting the ring 112, the swash plate 110 is at the minimum inclination position.
Several cylinder bores 113 are located about the drive shaft 103 in the center housing member. A piston 116 is reciprocally housed in each cylinder bore 113 and coupled to the swash plate 110. Rotation of the drive shaft 103 is converted into reciprocation of each piston 116 by the lug plate 109, the hinge mechanism 111 and the swash plate 110. As each piston 116 reciprocates, refrigerant gas is drawn to a compression chamber defined in the associated cylinder bore 113 through a corresponding suction valve, a number of which are formed in the valve plate 117 in correspondence with the bores 113. The refrigerant is then compressed and discharged to the discharge chamber 115 through a corresponding discharge valve, a number of which are formed in the valve plate 117 in correspondence with the bores 113.
A through hole is defined in the center housing member to receive an end of the drive shaft 103. A coil spring 118 is located in the through hole between the end of the drive shaft 103 and the valve plate 117. The spring 118 urges the drive shaft 103 leftward as viewed in FIG. 6 and compensates for dimensional errors of the parts, which prevents axial chattering in the compressor.
The crank chamber 102 is connected to the suction chamber 114 by a bleed passage 119. The discharge chamber 115 is connected to the crank chamber 102 by a supply passage 120. The supply passage 120 is regulated by an electromagnetic control valve 121. Specifically, the control valve 121 adjusts the opening size of the supply passage 120 to change the flow rate of highly pressurized refrigerant gas flowing from the discharge chamber 115 to the crank chamber 102. Since the flow rate of refrigerant flowing from the crank chamber 102 to the suction chamber 114 through the bleed passage 119 is lower than that of the refrigerant flowing through the supply passage 120, the difference between pressures acting on the front and rear ends of each piston 116, in other words, the difference between the pressure in the crank chamber 102 and the pressure in the compression chambers, is changed. Accordingly, the inclination angle of the swash plate 110 is changed, which changes the stroke of each piston 116. The displacement of the compressor is varied, accordingly.
A controller 131 includes a microprocessor and controls the electromagnetic clutch 105 and the control valve 121 based on external information. The information includes the passenger compartment temperature detected by a temperature sensor 132, the target temperature set by a temperature adjuster 133, which is manipulated by a passenger, and the ON/OFF state of an air-conditioner switch 134, which is manipulated by an passenger for starting and stopping the air conditioner.
FIG. 7 illustrates the control valve 121. The control valve 121 has a valve housing 126, a valve body 122, springs 125a, 125b and a solenoid coil 124. The valve housing 126 has a port 127, which is connected to the crank chamber 102 by a section of the supply passage 120, a valve chamber 128, which is connected to the discharge chamber 115 by another section of the supply passage 120, and a valve hole 120a, which connects the valve chamber 128 with the port 127. The valve body 122 opens and closes the valve hole 120a. The spring 125a extends between a wall of the valve chamber 128 and the valve body 122. The spring 125b, the force of which is weaker than that of the spring 125a, is located below the valve body 122.
When no current is supplied to the coil 124, the valve body 122 is moved downward by the force of the spring 125a, which completely shuts the supply passage 120. When a current is supplied to the coil 124, the valve body 122 is moved upward against the force of the spring 125a, which fully opens the supply passage 120.
When a passenger turns the switch 134 off, the controller 131 stops current to the electromagnet 108, which disengages the clutch 105. Accordingly, the compressor is stopped. At the same time, current to the coil 124 is stopped, which causes the control valve 121 to fully close the supply passage 120.
When the supply passage 120 is fully closed, the pressure in the crank chamber 102 is relatively low. Therefore, if the switch 134 is turned off in this state, the compressor is stopped with the swash plate 110 located at the maximum inclination position, which is shown by solid lines in FIG. 6. If the compressor is started immediately thereafter, the compressor starts operating with the maximum displacement, which requires the maximum load torque. This increases the load on the engine Eg. Accordingly, a great shock is produced.
Accordingly, it is an objective of the present invention to provide a vehicle air conditioner that produces no shock when a compressor is started immediately after it is stopped.
To achieve the foregoing and other objectives, the present invention provides an air conditioner for a vehicle having a variable displacement compressor and a controller. The compressor is selectively engaged and disengaged with the power source by an electromagnetic clutch and has a crank chamber accommodating a cam plate. The inclination angle of the cam plate varies based on the pressure of the crank chamber. A piston is coupled to the cam plate to reciprocally move by a stroke based on the inclination angle of the cam plate to compress gas within a compression chamber and discharge the compressed gas to a discharge chamber. The controller controls the displacement of the compressor based on an output from a detector sensing external conditions related to air conditioning. The compressor includes a supply passage connecting the discharge chamber to the crank chamber and an electromagnetic valve, which includes a valve body, for mechanically adjusting the cross sectional area of the supply passage to vary the pressure in the crank chamber and an electric actuator for selectively opening and closing the valve body. The controller selectively engages and disengages the electromagnetic clutch with the compressor, according to the output of the detector, outputs electric current according to the displacement of the compressor, and stops the current within a predetermined time period when the electromagnetic clutch is disengaged.